EP 0 277 129 B discloses a straw chopper that comprises a housing with opposing knives and a rotatable rotor arranged therein. Pairs of chopper knives are suspended in pendular fashion from the rotor, wherein the leading edges of the chopper knives are provided with beveled faces that form sharp edges. In order to control the direction of distribution and the dispersion width of the chopped straw, the beveled faces of the suspended chopper knife pairs are arranged in an alternating configuration such that the beveled faces either point toward or away from each other. Thus, the chopper knives have a trapezoidal or rhomboidal cross section.
During the chopping process, this geometry leads to bending moments in the chopper knife, which cause vibrations that reduce the service life due to fatigue fractures.
DE 36 26 456 A proposes a straw chopper, in which pairs of knives are also arranged in pendular fashion on a rotor. The leading edges of the chopper knives are ground on one side so as to deflect the chopped straw in the desired direction. In order to ensure that the straw is thrown toward the rear rather than outwards in the central region of the chopper drum, chopper knives ground on both sides are provided at this location. In addition, the grinding configuration of the chopper knives may be realized such that it makes a transition from the edge ground on one side to the edge ground on both sides from the sides of the rotor toward the center. In one embodiment, the outer end face of the chopper knives has a convex radius. The chopper knives have cutting edges on the leading and trailing edges. In order to ensure that the alignment of the cutting edges remains the same after they are worn and must be turned around and that the ejecting direction remains constant, the cross-sectional surfaces of the chopper knives are arranged radially symmetric with respect to the longitudinal axis. With respect to asymmetric knives that are ground on both sides, this means that the shorter, leading ground section is respectively arranged on the opposite side face of the chopper knife relative to the shorter, trailing ground section of the chopper knife.
Aerodynamic influences also cause bending moments to be generated in chopper knives with this geometry, where these bending moments generate vibrations that shorten the service life of the chopper knife. In addition, the continuously varying grinding configuration of the chopper knives has the disadvantage that a large number of different chopper knives is required. This negatively affects the manufacture, shipping and storage of such chopper knives.
DE 36 31 485 A describes a straw chopper with chopper knives, the geometry of which corresponds to that of the chopper knives according to DE 36 26 456 A, except that the grinding configuration of the cutting edges consists of a serration in this case.